Concentration Of Au Precursor Research Articles

Design of a gold clustering site in an engineered apo-ferritin cage

Water-soluble and biocompatible protein-protected gold nanoclusters (Au NCs) hold great promise for numerous applications. However, design and precise regulation of their structure at an atomic level remain challenging. Herein, we have engineered and constructed a gold clustering site at the 4-fold symmetric axis channel of the apo-ferritin cage. Using a series of X-ray crystal structures, we evaluated the stepwise accumulation process of Au ions into the cage and the formation of a multinuclear Au cluster in our designed cavity. We also disclosed the role of key residues in the metal accumulation process. X-ray crystal structures in combination with quantum chemical (QC) calculation revealed a unique Au clustering site with up to 12 Au atoms positions in the cavity. Moreover, the structure of the gold nanocluster was precisely tuned by the dosage of the Au precursor. As the gold concentration increases, the number of Au atoms position at the clustering site increases from 8 to 12, and a structural rearrangement was observed at a higher Au concentration. Furthermore, the binding affinity order of the four Au binding sites on apo-ferritin was unveiled with a stepwise increase of Au precursor concentration.

Highly sensitive near-infrared SERS nanoprobes for in vivo imaging using gold-assembled silica nanoparticles with controllable nanogaps

BackgroundTo take advantages, such as multiplex capacity, non-photobleaching property, and high sensitivity, of surface-enhanced Raman scattering (SERS)-based in vivo imaging, development of highly enhanced SERS nanoprobes in near-infrared (NIR) region is needed. A well-controlled morphology and biocompatibility are essential features of NIR SERS nanoprobes. Gold (Au)-assembled nanostructures with controllable nanogaps with highly enhanced SERS signals within multiple hotspots could be a breakthrough.ResultsAu-assembled silica (SiO2) nanoparticles (NPs) (SiO2@Au@Au NPs) as NIR SERS nanoprobes are synthesized using the seed-mediated growth method. SiO2@Au@Au NPs using six different sizes of Au NPs (SiO2@Au@Au50–SiO2@Au@Au500) were prepared by controlling the concentration of Au precursor in the growth step. The nanogaps between Au NPs on the SiO2 surface could be controlled from 4.16 to 0.98 nm by adjusting the concentration of Au precursor (hence increasing Au NP sizes), which resulted in the formation of effective SERS hotspots. SiO2@Au@Au500 NPs with a 0.98-nm gap showed a high SERS enhancement factor of approximately 3.8 × 106 under 785-nm photoexcitation. SiO2@Au@Au500 nanoprobes showed detectable in vivo SERS signals at a concentration of 16 μg/mL in animal tissue specimen at a depth of 7 mm. SiO2@Au@Au500 NPs with 14 different Raman label compounds exhibited distinct SERS signals upon subcutaneous injection into nude mice.ConclusionsSiO2@Au@Au NPs showed high potential for in vivo applications as multiplex nanoprobes with high SERS sensitivity in the NIR region.Graphical

Structural evolution and Au nanoparticles enhanced photocatalytic activity of sea-urchin-like TiO2 microspheres: An X-ray absorption spectroscopy study

Au nanoparticles decorated on titanium dioxide sea-urchin-like microspheres (TSUMs) were synthesized by a hydrothermal method. Having the gold nanoparticles well decorated on the crystalline spines of TSUMs are expected to increase the photocatalytic activity. XAS results indicate that different Au precursor concentration affects the electronic structure of the TSUM spines. The oxygen defects in the local structural symmetry of TiO6 octahedral are also shown to be strongly correlated with the decoration of Au nanoparticles, as testified by XAS analysis. The oxygen defects and Ti3+ in the spines, generated by the decoration of Au nanoparticles, are considered to enhance photocatalytic degradation of paracetamol. Further, in-situ XAS measurements reveal the hot electron transferred from Au to TSUMs assisted by the localized surface plasmon resonance under visible light irradiation. The investigation provides new insights into the active sites, surface’s structure, and its electronic properties of a photocatalyst applicable to environmental problems.

Unusual Stability and Catalytic Activity of Gold Nanoparticles in Polyoxyethylene Cholesteryl Ether.

We report a simple and spontaneous method for creation of extremely stable and catalytically active gold nanoparticles (AuNPs) from polyoxyethylene cholesteryl ether (ChEO15) and sodium tetrachloroaurate (III) dihydrate (Na[AuCl₄] · 2H₂O). AuNPs with uniform size and distribution were prepared at 27 °C (AuNPs were formed in <3 h) and at 50 °C (AuNPs were formed in <1 h). Our elucidations propose that creation of well-defined AuNPs is assisted by reductive ChEO15 surfactant solution via complexation and in-situ reduction of AuCl-₄ ions in which ChEO15 acts both as a reducing and consequently a stabilizing (capping) moiety. AuNPs size can be altered by suitably choosing the Au precursor concentration. The resulting AuNPs reveal outstanding catalytic activity for conversion of nitrophenols to aminophenol in the presence of NaBH₄ and also exhibit synthetic peroxidase-like activity. This simple yet effective synthesis technique opens prospect for creation of stable and active AuNPs.

Sensitive Chronocoulometric Detection of miRNA at Screen-Printed Electrodes Modified by Gold-Decorated MoS2 Nanosheets.

Developing novel simple and ultrasensitive strategies for detecting microRNAs (miRNAs) is highly desirable because of their association with early cancer diagnostic and prognostic processes. Here a new chronocoulometric sensor, based on semiconducting 2H MoS2 nanosheets (MoS2 NSs) decorated with a controlled density of monodispersed small gold nanoparticles (AuNPs@MoS2), was fabricated via electrodeposition, for the highly sensitive detection of miRNA-21. The size and interparticle spacing of AuNPs were optimized by controlling nucleation and growth rates through the tuning of deposition potential and Au precursor concentration and by getting simultaneous feedback from morphological and electrochemical activity studies. The sensing strategy, involved the selective immobilization of the thiolated capture probe DNA (CP) at AuNPs and hybridization of CP to a part of the miRNA target, whereas the remaining part of the target was complementary to a signaling nonlabeled DNA sequence that served to amplify the target upon hybridization. Chronocoulometry provided precise quantification of nucleic acids at each step of the sensor assay by interrogating [Ru(NH3)6]3+ electrostatically bound to phosphate backbones of oligonucleotides. A detailed and systematic optimization study demonstrated that the thinnest and smallest MoS2 NSs improved the sensitivity of the AuNP@MoS2 sensor, achieving an impressive detection limit of ≈100 aM, which is 2 orders of magnitude lower than that of a bare Au electrode and also enhanced the DNA-miRNA hybridization efficiency by 25%. Such an improved performance can be attributed to the controlled packing density of CPs achieved by their self-assembly on AuNPs, large interparticle density, small size, and intimate coupling between AuNPs and MoS2. Alongside the outstanding sensitivity, the sensor exhibited an excellent selectivity down to femtomolar concentrations, for discriminating a complementary miRNA-21 target in a complex system composed of different foreign targets including mismatched and noncomplementary miRNA-155. These advantages make our sensor a promising contender in the point of care miRNA sensor family for medical diagnostics.

One-Step Synthesis of Size-Tunable Gold@Sulfur-Doped Graphene Quantum Dot Nanocomposites for Highly Selective and Sensitive Detection of Nanomolar 4-Nitrophenol in Aqueous Solutions with Complex Matrix

In this study, a simple one-step synthesis procedure for the fabrication of a gold nanoparticle (Au NP)@sulfur-doped graphene quantum dot (Au@S-GQD) with tunable size was developed for the sensitive and selective detection of 4-nitrophenol in water and wastewater with a complex matrix. The particle size of two to six layered S-GQD is in the range of 1–7 nm with a mean diameter of 4.0 ± 0.5 nm. The S-GQD serves as a reducing agent for both Au ions and 4-nitrophenol reduction to generate Au@S-GQD nanocomposites as well as to produce the absorption signal of 4-aminophenol at 307 nm. The particle size of Au@S-GQD is tunable by simply adjusting the Au precursor concentration, and the mean diameter increases from 5 to 25 nm when the Au precursor concentration increases from 50 to 200 μM. Moreover, the Au@S-GQD nanocomposite exhibits good UV–visible absorption properties, and the change of wavelength ratio between 307 and the SPR peak of Au at 530 nm (A307/A530) is used to detect nanomolar levels of 4-nitropheno...

A highly conducting flower like Au nanoparticles interconnected functionalized CNFs and its enhanced electrocatalytic activity towards hydrazine through direct electron transfer

Abstract A numerous number of carbon-based nanomaterials have been developed for various technological applications, nevertheless a degree of accessibility is very less. Notably, carbon nanofibers (CNFs) based materials are insufficiently studied compare to CNT and graphene due to their inaccessibility in aqueous dispersion. Here we have functionalized the CNF by using acid treatment for further modification. Functionalization of CNF was confirmed by different characterization techniques like FT-IR, RAMAN, and XRD. To increase the electrical conductivity of F-CNFs, flower-like Au nanoparticles were electrodeposited onto the F-CNFs. Optimization study for electrodeposition of Au nanoparticles was performed with Au precursor's concentration and deposition cycle number. As the result, the optimal electrochemical active surface area (EASA) of the modified electrode is obtained to be 1.67 cm2 for 20 cycles which are higher than that of the previously reported Au nanoparticles based literature. The developed material was used as an electrode modifier for the detection of hydrazine. As expected, the amperometric hydrazine sensor shows a very low detection limit of 8 nM with a high sensitivity of 7.5 µA µM−1 cm−2. The excellent analytical parameters of the F-CNF@Au/GCE modified electrode over the various related modified electrodes suggest that the electrode can be useful for use in trace level detection of hydrazine in several industrial and pharmaceutical applications.

Aging Study of Gold Nanoparticles Functionalized with Chitosan in Aqueous Solutions

We studied the way in which stability and physicochemical properties of gold (Au) nanoparticles (NP) coated with chitosan are influenced by the molecular weight of chitosan and Au precursor concentration when samples are subjected to aging. Pharmaceutical use of AuNPs coated with chitosan is closely related to stability and physicochemical properties in relation to storage conditions and processing. For this purpose, series of AuNPs of different sizes were prepared by aqueous chemical reduction method using chitosan with various molecular weights as template. The physicochemical properties and stability at room temperature of AuNPs in aqueous solutions of chitosan have been investigated by following the temporal evolution of surface plasmon absorbance, Zeta potential, average dimension, and Au-chitosan interaction, after synthesis and through a period of 24 months. In our experiment, during the observed aging period, the AuNPs coated with chitosan presented a better colloidal stability, while using chitosan with medium molecular weight and medium concentration of Au precursor.

Enhanced catalyst activity by decorating of Au on Ag@Cu2O nanoshell

We successfully synthesized Au-decorated Ag@Cu2O heterostructures via a simple galvanic replacement method. As the Au precursor concentration increased, the density of the Au nanoparticles (NPs) on the Ag@Cu2O surface increased, which changed the catalytic activity of the Ag@Cu2O-Au structure. The combination of Au, Ag, and Cu2O exhibited excellent catalytic properties, which can further effect on the catalyst activity of the Ag@Cu2O-Au structure. In addition, the proposed Ag@Cu2O-Au nanocomposite was used to transform the organic, toxic pollutant, 4-nitrophenol (4-NP), into its nontoxic and medicinally important amino derivative via a catalytic reduction to optimize the material performance. The proposed Au-decorated Ag@Cu2O exhibited excellent catalytic activity, and the catalytic reduction time greatly decreased (5 min). Thus, three novel properties of Ag@Cu2O-Au, i.e., charge redistribution and transfer, adsorption, and catalytic reduction of organic pollutants, were ascertained for water remediation. The proposed catalytic properties have potential applications for photocatalysis and localized surface plasmon resonance (LSPR)- and peroxidase-like catalysis.

Synthesis of Ultralong, Monodispersed, and Surfactant-Free Gold Nanowire Catalysts: Growth Mechanism and Electrocatalytic Properties for Methanol Oxidation Reaction

The understanding of factors influencing the growth of nanowires is critical for the precise control of the nanowire morphologies and the design of active nanowire catalysts for fuel cell reactions. While the formation of gold nanoparticles followed by self-assembly into short strings of nanowires is known, little is understood in terms of the control of the morphologies and surface properties toward enhanced electrocatalytic properties. This report describes novel findings of an investigation of the growth mechanism of ultralong, highly monodispersed, and surface surfactant-free gold nanowires (Au NWs) synthesized by a galvanic replacement reaction of Te NWs as an initial template. By manipulating reaction time and Au precursor concentration, an aggregative growth mechanism in terms of 1D and 3D growth pathways for the NW length and diameter, respectively, is revealed to be operative in the template-directed Au NW formation process, shinning some fresh insight into the controllability of the nanowire mor...

Effect of the preparation method of supported Au nanoparticles in the liquid phase oxidation of glycerol

Catalytically-active gold nanoparticles that are stable in aqueous solution have been prepared by sodium borohydride reduction of the respective metal salts in the presence of the stabilising polymer PVA (polyvinylalcohol). By controlling the ratio of the polymer to the metal, nanoparticles with different particle size and size distribution were synthesised. By varying the concentration of the gold and PVA/Au wt/wt ratio, well-defined nanoparticles with mean diameters from 3 to 5nm could be fabricated. In general increasing the concentration of Au precursor, bigger particles size were obtained. Furthermore decreasing the amount of PVA, bigger particles were obtained, with the exception of the catalysts synthesized in presence of a large amount of PVA (PVA/Au=2) wt/wt. Probably, in presence of an excess of protective agent, the immobilization of the Au nanoparticles onto the support is more difficult, leading to partial aggregation and coalescence of Au. In addition, the studies on the effect of heat pre-treatment revealed a higher resistance to aggregation of Au nanoparticles supported on titania than on activated carbon. A selected series of the synthesised supported materials were studied in the liquid phase oxidation of glycerol with the purpose of correlating catalytic activity and selectivity with particle size and metal choice. We demonstrated that by both particles size and amount of protective agent strongly influence the activity and selectivity.

DNA Hydrogel as a Template for Synthesis of Ultrasmall Gold Nanoparticles for Catalytic Applications

DNA cross-linked hydrogel was used as a matrix for synthesis of gold nanoparticles. DNA possesses a strong affinity to transition metals such as gold, which allows for the concentration of Au precursor inside a hydrogel. Further reduction of HAuCl4 inside DNA hydrogel yields well dispersed, non-aggregated spherical Au nanoparticles of 2-3 nm size. The average size of these Au nanoparticles synthesized in DNA hydrogel is the smallest reported so far for in-gel metal nanoparticles synthesis. DNA hybrid hydrogel containing gold nanoparticles showed high catalytic activity in the hydrogenation reaction of nitrophenol to aminophenol. The proposed soft hybrid material is promising as environmentally friendly and sustainable material for catalytic applications.

Single gold-nanoparticles-decorated silver/carbon nanowires as substrates for surface-enhanced Raman scattering detection

Silver/carbon (Ag/C) core–shell nanowires with different thickness of shell were synthesized by a hydrothermal method and used as templates for fabricating gold nanoparticle-decorated Ag/C (Ag/C/AuNPs) nanowires. The Ag/C/AuNPs nanowires were characterized by transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM), and energy-dispersive X-ray (EDX). It was found that the number density and particle size of Au nanoparticles can be tuned by varying the concentration of Au precursor. Surface-enhanced Raman scattering (SERS) measurements showed that single Ag/C/AuNPs nanowire exhibited strong SERS effect. Rhodamine 6G (R6G) molecules, with an extremely low concentration (1.0 × 10−11 M), were readily detected using single Ag/C/AuNPs nanowires. Detection of melamine molecules at concentrations as low as 1.0 × 10−7 M was used as an example to show the possible application of such Ag/C/AuNPs nanowires. In addition, the effect of benzoic acid on the detection of melamine was also investigated. It was found that the SERS spectrum profile and intensity of melamine is very sensitive to the presence of benzoic acid.

One dimensional Ag/Au/AgCl nanocomposites stemmed from Ag nanowires for electrocatalysis of oxygen reduction

This paper reports the synthesis and characterization of one dimensional nanocomposites composed of Ag, Au, and AgCl (denoted as Ag/Au/AgCl). The Ag/Au/AgCl composites with different compositional ratios are prepared by the galvanic replacement reaction between a Ag nanowire template and Au precursor at various concentrations (1, 10, 100 mM HAuCl4). As the Au precursor concentration increases, the structure of the resulting Ag/Au/AgCl changes from a core–shell solid wire to a porous hollow wire with a decrease in the Ag and AgCl contents and increase in the Au content. The catalytic activity of Ag/Au/AgCl for the oxygen reduction reaction (ORR) is investigated in 0.1 M NaOH solution. The nanocomposite with a Ag : Au : AgCl compositional ratio of 4 : 86 : 10 shows reasonable ORR activity (high ORR current, positive onset potential) along with sufficient stability and ethanol tolerance in alkaline media, suggesting that it could be used as a substitute for Pt-based cathode catalysts in fuel cells.

ZnO/Au Composite Nanoarrays As Substrates for Surface-Enhanced Raman Scattering Detection

Well-aligned ZnO nanoneedle and nanorod arrays were grown on an aluminum-doped zinc oxide (AZO) buffer layer by chemical vapor deposition and used as templates for making gold-coated ZnO (ZnO/Au) composite nanoarrays. The coverage of Au nanoparticles on ZnO nanoneedle and nanorod was controlled by varying the concentration of Au precursor. High coverage led to the formation of ZnO/Au nanoneedle bundles. The ZnO/Au composite nanoarrays were applied as substrates in surface-enhanced Raman scattering (SERS) measurement. The SERS enhancement factor is mainly controlled by gold coverage and morphologies of the ZnO/Au nanoarrays. Their application in rapid detection of melamine in egg white is demonstrated. This SERS-based melamine detection is advantageous in that sample pretreatment is not needed. It showed the potential of the ZnO/Au nanoarrays as a convenient and robust SERS-active substrate for food safety monitoring.

Preparation of gold-silica heterogeneous nanocomposite particles by alcohol-reduction method

Au-silica heterogeneous nanocomposite particles were prepared by novel preparation strategy involving alcohol-reduction method using 3-aminopropyltrimethoxysilane (APTMS) as a binder between silica surface and Au nanoparticles, and using PVP as a stabilizer for Au nanoparticles. The evolution of morphology of composite particles was investigated with increasing reaction time at different Au precursor concentrations of 100 ppm and 250 ppm using UV–vis spectrophotometer and TEM. It is shown that the size of immobilized Au particles on silica surface can be controlled with the variation of reaction rate via adjusting Au precursor concentration and reaction time, but the high concentration of Au precursor hinders the immobilization of well-defined Au nanoparticles due to the slow reduction rate of Au precursor. On the basis of experimental results, the role of APTMS and PVP on the formation of composite particles and the effect of Au precursor concentration on the morphological evolution of composite particles are briefly discussed.